High amperage molded case circuit breakers are required to interrupt large values of current extended through a plurality of downstream breakers to respective loads. Problems of course arise both from the blade and contact mass required to carry the large current values and the forces required for the closure of the contacts necessitate a relatively large closing spring.
A closing spring is required to store energy for contact closure in the event the breaker is tripped and power lost and the closing spring must be large to close the contacts against the force of the overtravel springs which initially tend to resist contact opening in response to a momentary current rise or surge. The closing spring which is used to provide the contact closing energy is generally charged or tensed through a mechanism under control of either an electrically driven motor or a manually operable link arrangement and then released to erect a toggle assembly, which moves the blades through blade carriers into a contact closed position.
It is customary in breakers of the described type to maintain the closing spring tensed so that after each discharge, the closing spring is recharged. This enables the contacts to again be closed after having been tripped open or manually opened, and avoids the need for an electrical power source to close the contacts after tripping. An interlock however must be provided to prevent inadvertent discharge of the closing spring if the contacts are already closed to avoid possible damage or if the breaker is being held tripped.
Electronic circuitry is also provided in breakers of the described type for momentarily operating a trip solenoid to release a latch for enabling collapse of the toggle assembly to open the contacts, but arrangements for interconnecting the trip solenoid with the other apparatus are expensive and the solenoid must be reset after such operation requiring considerable power. Such power is not easily provided by the trip solenoid as the solenoid is normally held in its unoperated condition by a permanent magnet